Skin comprises at least four distinct layers of tissue: the nonviable epidermis (i.e., the stratum corneum), the viable epidermis, the dermis, and subcutaneous connective tissue and fat. The circulatory system lies in the dermis and tissues below the dermis. As skin generally prohibits the transport of macromolecules to the dermis and tissues below the dermis, needles are often required to administer macromolecular medicants.
Ultrasound has long been used for diagnostic imaging applications. More recently however, several new therapeutic applications for ultrasound are being discovered. Among the applications for ultrasound, enhanced transdermal medicant delivery and/or effectiveness has received considerable attention. To date, however, the better part of ultrasound-enhanced medicant delivery and/or effectiveness efforts have been focused on ultrasound at frequencies below 200 kHz, and prior systems have directed ultrasound at single layers of tissue.